The present invention relates to a marine anchor.
Better and higher performance standards are being demanded of marine anchors due to the increased needs of large ships, offshore drilling platforms, and anchored floating installations.
In general, the anchors presently used are of a reversible type (can anchor from either side) and consist of a shank fixed by its front portion to a chain and having on its rear portion a transverse pivot joint around which two generally coplanar flukes can pivot simultaneously, the flukes being more or less triangular in shape. When these anchors are placed on the bottom, their back end is raised, for instance by a base part of the anchor, and the two flukes tend under the influence of their weight to tilt forwardly toward the bottom around the pivot. A pull on the shank thus tends to drive the flukes into the sea bed.
The disadvantage of these known anchors is that when they are buried, they exert a basically upward strain on the sea bottom, which tends to lift up the thin layer of earth covering the feet resulting in a comparatively reduced anchorage force.
Anchors having the shape of a ploughshare, as for example in French Pat. No. 2,046,966, have already been designed in an attempt to increase the anchorage force. These anchors have the general shape of a ploughshare of generally triangular cross-section, its size increasing from the front end so that the side surfaces of the ploughshares are inclined to face the side and the top. These ploughshares are mounted on bars or on shanks, both pivotally and non-pivotally.
However, these latter anchors have not given complete satisfaction.
On the one hand, their side surfaces have more or less horizontal portions which also tend to lift the earth upwardly.
On the other hand, they are not reversible and must therefore either be provided with supplementary methods, for example a shank made of two pivoted portions, to enable them to be properly positioned on the bottom, or must be placed by special means such as floating cranes, ships, and floats, but with no guarantee that the proper positioning will always result.
Anchors mounted in a frame and having two pivoted flukes able to move freely around slightly convergent axes have also been suggested, as in U.S. Pat. No. 3,977,351. Such anchors are relatively complicated to build and do not yield a significantly increased anchorage force since the flukes which are poorly guided or, if pivoted between themselves, tend to position themselves in planes little different from each other, and the frame interferes with the digging in of the anchor.
Finally, as in U.S. Pat. No. 2,380,119, anchors have been suggested in which the two flukes are pivoted independently of each other around a common axis following the geometric axis of the anchor and mounted on a base, the shank itself being pivoted with respect to this base around an axis perpendicular to the preceding axis. This arrangement significantly increases the anchorage force and has all the advantages of reversibility. The disadvantage of these anchors is that they are more complicated to build and the flukes do not obtain maximum penetration.